Skip to main content

Full text of "The manufacture and properties of iron and steel"

See other formats

208                         METALLURGY OF IRON AND STEEL.
temperature, because the slag is not stable and at a higher temperature the hearth would be cut away, the reactions would be more violent and the phosphorus would leave the slag and go back into the metal. In the open-hearth furnace the phosphorus does not go back, because the slag contains a sufficient proportion of lime to make a permanent compound with the phosphorus, so that it is not readily reduced by carbon. Such a slag needs a high temperature for complete fusion and this temperature cannot well be carried in the washed, metal furnace,                              . -,.,
" (3) The washed metal furnace is tapped when the metal contains about, 2 per cent, of carbon, because if the carbon be run down any lower a much higher temperature would be needed, and because this kind of product suits the demands of the trade.            ,; .
The low-phosphorus open-hearth steel of former days was made from either low-phosphorus pig-iron and charcoal blooms or washed metal and charcoal blooms, and this washed metal was the product of a basic process. The charcoal blooms were also of basic origin, because they were-made by. the action of a basic oxidizing slag on melted metal.
After the, introduction of the basic open-hearth process it became 'possible to buy in the open market a supply of low-phosphorus .steel scrap at a moderate price, and this scrap rapidly took the place of the high-priced charcoal blooms and stopped their manufacture. Thus while the basic open-hearth furnace rendered it possible to produce a low-phosphorus steel much cheaper than it had ever been produced before, it also cheapened the cost of low-phosphorus acid open-hearth steel. This is true, however, only to a certain extent, 'for the basic 'furnaces themselves need scrap and use most' of th.e available supply. Moreover, the .low-phosphorus pig-iron, 'which must be used, costs from three to five dollars per ton more than the ordinary Bessemer grade.
In order to overcome these difficulties we have introduced at the works of The Pennsylvania Steel Company an. adaptation of the old washed metal process. The pig-iron is charged in a basic lined furnace, and almost all of the silicon and phosphorus and part ' of the sulphur and carbon are eliminated. At this stage it is washed, metal, and in olden times would have been run out in chills and afterward charged into the acid furnace, but in this new practice it is poured into a ladle, and, while still fluid, is poured into the